Ladder lock



Mal-ch24, 1942. 7 1 5 DAHLBERG I 2,277,392

LADDER LOCK Filed Aug. 20, 1940 Patented Mar. 24, 1942 LADDER LOCK Arnold E. Dahlberg, New Bedford, Mass.

Application August 20, 1940, Serial No. 353,424

1 Claim.

This invention relates to improvements in locks for extension ladders and has for an object the provision of a lock which may be simply and inexpensively constructed, and operated with relatively little eifort and with a minimum of wear and damage to the ladder with which it is associated.

Ladder locks hereinbefore employed for the retention of relatively displaceable ladder sections in extended relation have consisted of a support for attachment to one ladder section, usually in the form of a housing, and hook and latch members pivotally mounted on the support, the hook member being arranged for engagement with the rungs of the associated ladder section, and the latch member serving to withdraw the hook member from the path of movement of the rungs to permit collapsirlg or telescoping the ladder sections. It is with this type of ladder lock that the instant invention is concerned, certain changes being effected in the structure and relation of the hook and latch members whereby the utility of the lock is greatly enhanced.

Specifically, the invention contemplates the provision of a hook member which is so pivotally supported with relation tothe direction of displacement of the ladder sections that there is no tendency to wedge or bind the engaged rungs,

and a latch member comprising a bell crank lever having one arm extending into the path of the engaged rungs, the other arm engaging the hook member to withdraw the latter to permit collapse of the ladder. The arrangement of the cooperating members is such that the leverage exerted thereon by the rungs is relatively high, whereby damage to the rungs during both extension and collapse of the ladder is minimized.

Further objects and features of the invention will be apparent from the following description taken in connection with the accompanying drawing, in which Figure 1 is a front elevation of an extension ladder, illustrating one method of employing the 2 improved lock;

Figure 2 is a longitudinal section through the lock housing, showing the hook member in engagement with a ladder rung;

Figure 3 is a similar sectional view showing the hook member in retracted position during collapse of the ladder sections;

Figure 4 is a sectional view on the line 4-4 of Figure 2 showing the lock housing mounted on a ladder section; and

Figure 5 is a view corresponding to Figure 2 but illustrating a slight modification.

In order to facilitate an understanding of the invention, reference will be made to the embodiments thereof illustrated in the accompanying drawing and specific language will be employed. It will nevertheless be understood that various further modifications of the devices illustrated herein, such as would fall within the province of those skilled in the art to construct are contemplated as part of the present invention.

Referring now to Figure 1 of the drawing, which illustrates one method of using the ladder lock described herein, it will be noted that a pair of locks ID are secured to the inner faces of the side rails H of an upper ladder section indicated generally at l2, the locks being positioned for cooperative engagement with the rungs l3 of the lower ladder section indicated generally at M. Guide hooks l8, secured to the lower ladder section l5 and embracing the side rails ll of the upper ladder section l2 may be employed. The ladder may be extended in any conventional manner, for example by means of a rope 20 passing about a sheave 2!, carried by a rung of the lower ladder, one end of the rope being secured to a rung on the upper ladder.

The arrangement thus far described is con ventional and forms no essential part of the instant invention. Various alterations may be effected; for example, the locks may be mounted on the lower ladder section for cooperation with the rungs of the upper ladder section by inversion of the elements shown in Figure l.

The details of the lock are illustrated more particularly in Figures 2 to 4 inclusive. Thus each lock may comprise a support 25, preferably in the form of an elongated housing having an opening at one side thereof as shown at 26. Pivotally mounted on the support 25 and within the housing and projecting through the opening 26 thereof is a hook member 28, this hook member being formed at its free end to provide a rung-embracing or hook portion 30 for selective engagement with each of the several rungs of the lower ladder section. A fiat spring 3|, also mounted on the support 25, normally urges the hook member 28 outwardly through the opening 26 and into engagement with an abutment 33 formed on the support 25, so that the hook portion 3!) of the hook member 26 may engage the rungs l3 and thus prevent collapse or telescoping of the ladder sections.

In this connection it is important to note that the two arms of the hook portion of the hook member extend in a direction away from the fulcrum of the hook member. Thus as the ladder sections are extended, the rungs of the lower ladder section readily press the hook member inwardly and away from the path of movement of the rungs, since as the hook member is swung inwardly of the support 25, that portion of the hook member which is subjected to the camming action of the relatively moving rungs has a component of movement in the direction of movement of the rungs. Much less force is therefore required to displace the hook member inwardly than would be required if the fulcrum for the hook member were located adjacent the opposite end of the support 25.

Furthermore, it will be appreciatedthat because of this arrangement of the hook member, the application of force tending to collapse or telescope the ladder sections does not bind the rungs against the support or housing 25, as would be the case if the fulcrum for the hook member 28 were located below the hook portion 30 thereof.

A latch member 35 is also pivoted on the support or within the housing which comprises the same, this latch member having two arms indicated at 3B and 31 respectively. In the normal or looking position of the hook member 28, the arm 36 of the latch member 35 engages the inner arm of the hook portion of the hook member 28, and the arm 31 of the latch member extends outwardly into the path through which the rungs I3 of the lower ladder section are relatively displaced on extension or collapse of the ladder. The latch member is urged toward the position in which it is shown in full lines in Figure 2 by a fiat spring 38 mounted on the support 25 and engaging the arm 31 of the latch member. It will be observed that on extension of the ladder sections, the arm 31 of the latch member is engaged by the rungs I3 of the lower ladder section I4 and is swung to the position in which it is shown in dotted lines in Figure 2, movement of the latch member in the opposite direction under the action of the spring 38 being limited by engagement of the arm 36 of the latch member with one of the arms of the hook portion 30 of the hook member 28. On relative movement of the ladder sections in the opposite direction, during collapse of the ladder, the rungs I3 of the lower section engage the arm 31 of the latch member 35 and through the arm 35 of the latch member the hook member 28 is displaced inwardly. It will be noted in this connection that the leverage exerted by the latch member on the hook member is at all times favorable to smooth withdrawal of the hook member, the engagement of the hook member by the arm 36 of the latch member 35 being followed by contact between the arm 31 and the outer face of the hook member, as will be appreciated from an inspection of Figure 3 in which the parts are shown in the final releasing position as the ladder sections are collapsed. Again, by the use of a two-armed or bell crank latch member, this favorable leverage may be obtained without the employment of an excessively long support or housing 25, such as would be required if a latch member having only one arm were employed.

The operation of the device will be apparent from the foregoing description. Thus, assuming that the lock is mounted as shown in Figure 1 on an upper ladder section with the hook portion 30 of the hook member 28 extending downwardly, the outer face of the hook member 28 will be successively engaged by the several rungs I3 of the lower ladder section I4 and will swing inwardly out of the path through which these rungs are displaced with respect to the upper ladder section. When the ladder has been extended to the point desired, relative displacement of the ladder sections is interrupted immediately after one of the rungs I3 has passed below the hook portion 30 of the hook member 28, and before that rung has passed below the arm 31 of the latch member 35. Thus when the upper section I2 of the ladder moves downwardly, the rung I3 is engaged by the hook portion of the hook member, and further downward movement is thus prevented. If it is desired to collapse the ladder, the upper section is displaced upwardly so that the rung I3 previously engaged by the hook member passes just below the arm 31. The upper ladder section is then permitted to descend, and the hook member 28 is displaced inwardly so as to clear the rungs I3 of the lower ladder section I4 by the action of the latch member 35 as hereinbefore explained.

In Figure 4 is illustrated a preferred method of securing the support or housing 25 in position on a side rail II of a ladder section, bolts 39, extending through the side rail and through the fulcrums for the hook member 28 and latch member 35 respectively, being employed.

It will of course be understood that coil springs may be used to urge the hook member 28 and the latch member 35 to the positions normally occupied thereby. Furthermore, I have found that the complete elimination of springs from the lock, and especially the elimination of the spring for the latch member 35 is highly desirable in the interest of smooth operation and long life.

Such an arrangement is shown in Figure 5 of the drawing which illustrates a modified form of construction. In this form of the invention the essential elements of the lock are similar to those illustrated in the embodiment shown in Figures 2 to 4 inclusive and similar reference characters are employed to designate the same. Thus the hook member 28 may be formed to provide an inwardly directed arm 4I having a weighted portion 42, and the latch member is likewise provided with an arm 43 having a weighted portion 44. The arms M and 43, and the associated weighted portions are permitted to swing through an opening 45 in the support or housing 25.

It will be noted that in this arrangement the weighted portions of the movable members function in much the same manner as the springs 3! and 38 of the previously described embodiment but offer less friction to movement and are helpful in simplifying the structure. It is of course contemplated that either or both of the movable members may be urged to normal position by gravity in the manner illustrated in Figure 5.

It will be appreciated that the instant invention contemplates an improved ladder lock characterized by small size and weight, smoothness of operation, freedom from possibility of damage to the ladder rungs, and low cost of manufacture.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

In a lock for extension ladders having relatively displaceable ladder sections, the combination with a support for attachment to one of support for engaging and limiting outward movement of said hook member, a latch member pivotally mounted on said support and having two arms arranged for successive engagement with the respective rung-embracing arms of said hook member to displace the latter out of rung-engaging position, the pivotal aXes of said hook and latch members being disposed longitudinally of said sections at opposite sides of the hook portion of said hook member, and means normally retaining said hook member in rung-engaging position and said latch member in a position such that one of the arms thereof extends into the path of displacement of the rungs and the other arm thereof engages one of the rung-embracing arms of said hook member, said last named means including a Weighted portion on each of said members.

ARNOLD E. DAHLBERG. 

